IMPROVEMENTS IN ACUITY IN ADULT AMBLYOPES AFTER LASER IN
SITU KERATOMILEUSIS OR PHOTOREFRACTIVE KERATECTOMY.
Written by Kyle Sexton, OD
Richard Anderson, OD; Timothy Christianson, MD; Craig Finch, OD.
PURPOSE: To report the improvement in visual acuity in amblyopic adults after
receiving laser in situ keratomileusis (LASIK) or photorefractive keratectomy (PRK).
INTRODUCTION: Amblyopia: Amblyopia refers to a decrease of vision, either
unilaterally or bilaterally without any evidence to an organic cause of vision loss.i
Etiology: In general, amblyopia is believed to result from disuse due to inadequate foveal
or peripheral retinal stimulation and/or abnormal binocular interaction that causes
different visual input from the foveas. Most vision loss from amblyopia is preventable or
reversible with the right kind of intervention. The recovery of vision tends to depend on
the maturity of neural connections, the length of deprivation, and at what age the therapy
is begun.ii
Epidemiology: About 2% of the general population has amblyopia.i It is also the most
prevalent cause of monocular vision loss in adults. Furthermore, amblyopes have a
higher risk of becoming blind due to the potential loss of vision in the normally
functioning eye from outside causes.iii
Conventional Orthoptics: Conventional therapy for amblyopes consists of most accurate
spectacle correction possible, as well as full or part-time patching of the non-amblyopic
eye and/or atropine penalization. Vision therapy also provides adjunct treatment.ii
Close supervision of patients undergoing amblyopia therapy must be maintained to
ensure patient compliance, without which therapy is not successful. Outpatient follow-up
visits must continue far beyond the primary completion of treatment to anticipate and
prevent any regression from occurring.ii A study by Levartosky et al, however, showed
regression in visual acuity in 75% of children with anisometropia of 1.75 diopters or
more after occlusion therapy.iv
PAST STUDIES: Barequet et al. reported that LASIK improved visual acuity in
amblyopes, in a sampling of 8 eyes in 7 patients, with a mean patient age of 30±10 years
(range 21 to 49 yrs). After LASIK surgery, the range of best-corrected visual acuity,
which previously ranged from 20/32 to 20/80 now ranged between 20/20 to 20/30, and a
mean gain of 3 Snellen lines (range 2 to 4 lines) was observed.v
Sakatani et al. reviewed 21 amblyopic eyes of 18 patients and observed that 33.3%
gained one line of acuity after LASIK and 42.8% gained more than one line post
operatively.vi
METHODS: This study is retrospective review of adult patients previously diagnosed
with amblyopia, who underwent LASIK or PRK correction for their ametropia. Lasers
used were the Nidek EC-5000 and VISX S3/S4. Data and candidacy for the procedure
were based on manifest refraction, cyclopledged refraction, keratometry, pachymetry,
intraocular pressure, corneal topography, anterior segment evaluation, and dilated fundus
examination. Post-operative exams took place 1 day, 1 week, 1 month, 3 months, 6
months and 1 year after the initial procedure. All patients used an antibiotic and steroid
drop four times per day for 5 days, and preservative-free artificial tears for 4 times per
day for 1 month post-op. Manifest refractions and best-corrected visual acuity (BCVA)
were assessed at the 1 month, 3 months, 6 months, and 1 year post-op evaluations.
DIAGNOSTIC CRITERIA: For this study, amblyopia was assessed as a two or more
line difference of BCVA between eyes on a standard Snellen chart, or a BCVA of 20/40
or worse. All patients of this study had amblyopia due to anisometropia or high bilateral
refractive error. No strabismic amblyopes were included.iii
RESULTS: 23 eyes of 17 patients were included, with a mean patient age of 35 years
(range 23 to 52 yrs). Mean preoperative BCVA in the amblyopic eye was 20/48, ranging
from 20/30 to 20/80, with an average spherical component of –7.42 diopters sphere (DS)
(range -17.75 to +7.25), and an average cylindrical component of –2.47 diopters cylinder
(DC) (range –5.50 to 0.00). At 3 months post-op, the mean BCVA in the amblyopic eye
was 20/30, with a range of 20/40 to 20/20. The average spherical correction was +0.09
DS, with a mean cylindrical correction of –0.58 DC. On average, the amblyopic patients
gained 2 lines of acuity, but ranged from 1 to 4 lines of improvement. Each patient
reported significant subjective improvement and satisfaction with the results, and
continued to have stable acuity at the 6-month and annual check-up.
LASIK vs. PRK: Some patients had PRK as opposed to LASIK due to various factors
that made them better candidates for PRK, such as decreased corneal thickness and large
refractive error. LASIK patients (n=7) had an average initial BCVA of 20/44. At 3
months post-op this acuity had improved to an average of 20/29. PRK patients (n=16)
had an average initial BCVA of 20/70. At the 3 months check, the PRK patients had an
average BCVA of 20/40. Although the PRK patients on average gained 3 lines of acuity,
and the LASIK patients gained 1.5 lines, the ratio of improvement for PRK versus
LASIK was proportionally almost equal due to the initial BCVA of PRK patients being
lesser than that of the LASIK patients. The ratio of initial acuity versus post-op acuity in
LASIK patients was 0.66 while it was 0.57 in PRK patients. There was no significant
difference.
DISCUSSION:
As opposed to the findings on regression of acuity found by Levartosky et al. when
standard occlusion therapy was implemented, no regression in visual acuity has been
observed in any of the patients in this study.
By permanently correcting the amblyogenic refractive error, patients were provided with
constant focused visual stimuli, which effectively remediated their amblyopia, despite
conventional thought that adults with amblyopia cannot be effectively treated with
success.
Studies have shown that treatment of amblyopia after “visual maturity,” which occurs
around the age of 9, can improve not just visual acuity, but overall visual functioning.
Nevertheless, many clinicians do not treat amblyopia if patients appear “too old”.vii
Subjectively, all patients in this study expressed an improvement in quality of life after
having refractive surgery.
All results were attained without the use of vision therapy, and were based on a best
optical correction. The same correction that did not offer increased acuity when used
alone. The only factor in the patients’ vision that was altered was corneal thickness and
composition. It can be hypothesized; therefore, that photoabation of the cornea during
LASIK or PRK is physiologically altering not only the refraction of the patient, but any
corneal properties that prevent better acuity with refraction alone. Further studies on this
hypothesis can be accomplished by monitoring higher-order aberrations using
WaveScanTM technology before and after refractive surgery to determine if the newly
thinner cornea is increasing the possibility of improved acuity via physiological change
within the cornea itself, as opposed to refractive or neuronal limitations hindering acuity.
i
BARRET, BRENDAN T., BRADLEY, ARTHUR, MCGRAW, PAUL V. Understanding the Neural
Basis of Amblyopia. NEUROSCIENTIST 10(2):106-117, 2004.
ii
YEN, KIMBERLY G. Amblyopia. EMEDICINE. 08/16/2004:1-12.
iii
CALOROSO, E. E.; ROUSE, M. W.; Clinical Management of Strabismus. Butterworth & Heineman,
Stoneham, MA, 1993.
iv
LEVARTOVSKY S, OLIVER M, GOTTESMAN N, SHIMSHONI M. Factors affecting long term
results of successfully treated amblyopia: initial visual acuity and type of amblyopia. BR J
OPHTHALMOL. 1995 Mar;79(3):225-8.
v
BAREQUET, IRINA S. MD; WYGNANASKI-JAFFE, MD; HIRSCH, AMI, MD. Laser in situ
Keratomileusis Improves Visual Acuity in Some Adult Eyes with Amblyopia. JOURNAL OF
REFRACTIVE SURGERY. 20(1) Jan-Feb 2004.
vi
SAKATANI, KEIKO, MD; JABBUR, NADA S., MD; O’BRIEN, TERRENCE P., MD. Improvement in
Best Corrected Visual Acuity in Amblyopic Adult Eyes after Laser in Situ Keratomileusis.
vii
LEE, R. Active Vision Therapy on an Adult Strabismic Amblyope. JOURNAL OF BEHAVIORAL
OPTOMETRY, 10(5), 1999.